Edge-sensing mechanisms

ABSTRACT

The invention provides a sensitive sensor and system with low response inertia for maintaining the accuracy of the path of a moving web of material and includes in its construction means to facilitate maintenance without the need for subsequent adjustment.

United States Patent I Medding et a1. 1 Mar. 7, 1972 [54] EDGE-SENSING MECHANISMS [72] Inventors: Reuben Medding, North Caulfield, Vic- [56] References Cited toria; Graham Roland Tyson, Nunawad- UNlTED STATES PATE S ing, Victoria, both of Australia 3,244,340 4/ 1966 Fife et al ..226/22 Asslgneez Consolidated Electronics Propneta- 3,260,434 7/1966 Jacobsen.... ..226/22 x W Limited, Brunswick East, Victoria, A 3,407,706 10/1968 Ott, Jr ..226/22 X 3,490,674 1/1970 Ott, Jr. et a1. ..226/22 X [22] filed: 1969 Primary Examiner-Allen N. Knowles [21] Appl. No.: 879,085 Attorney-Wenderoth, Lind & Ponack A T [30] Foreign Application Priority Data [57] ABSTR c d h l The invention provides a sensitive sensor an system wit ow Nov. 29, 1968 Australla ..47045/68 response inertia for maintaining the accuracy of the path of a moving web of material and includes in its construction means [52] US. Cl ..226/22, 137/82 to facilitate maintenance without the need for subsequent d [51] Int. Cl ..B65h 25/08 justment [58] Field of Sear-c ..226/22; 73/37.7; 137/82, 83,

137/815 5Claims,9DrawingFigures PATENTEDHAR 7 :972 3,647,123

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EDGE-SENSING MECHANISMS This invention relates to edge-sensing mechanisms for use in the control of moving webs of material.

It is well known to use sensing devices in association with moving webs, the purpose being to detect any deviation of the moving web from a desired path and use a detection signal generated in response to web deviation to reposition the web accordingly. Various systems are in use and while moderately satisfactory suffer from lack of sensitivity and response inertia.

It is accordingly the principal objective of this invention to provide web edge-sensing means of improved sensitivity.

It is a further objective of the invention to provide web edge-sensing means for use in a web path control mechanism having a minimum of response inertia.

The term response inertia is used to define the time required for correction of the web path to be automatically effected after deviation.

A further defect of prior sensing systems is that maintenance, such as regular cleaning of the sensing means, normally results in the need for meticulous resetting of the sensing means with attendant increase in nonproductive running time.

It is accordingly a further objective of this invention to provide a web edge-sensing means capable of being readily dismantled for maintenance purposes such as cleaning without any need for adjustment after reassembly.

With the above-stated principal objective in view there is provided according to the invention an edge-sensing device comprising a body portion having an edge entry gap, a pair of ports in spaced juxtaposition in said edge entry gap, one of said ports being arranged to receive air discharged from the other port, valve means associated with the air-receiving port comprising diaphragm operable in response to air pressure in the receiving port to move a valve member in a valve body to control the flow of a pressurized fluid through the valve body, the operation of the device being such that movement of a web edge in the edge entry gap across the space between the ports causes responsive movement of the diaphragm and hence operation of the valve means. Conveniently the valve means is mounted on the body portion of the sensing means and comprises a valve chamber having a fluid inlet port and a fluid outlet port, a port communicating with atmosphere and a valve member movable within the chamber in response to movement of the diaphragm to supply fluid from the inlet port to the outlet port or vent the outlet port to atmosphere, and a duct within the body to permit fluid pressure from the outlet to be applied to the valve member to control its movement against the action of the diaphragm in such a manner that the valve stabilizes in position only when the upward force from the diaphragm balances the downward force on the valve member so produced.

To achieve a further objective of the invention the ports in the body portion may be fixed in a housing including at least part of the edge entry gap and removable from the body portion for maintenance purposes, and suitable locking means may be provided to accurately locate the port housing within the body portion without the need for further adjustment.

In operation one of the ports is connected with a source of compressed air and air discharged through this port is directed to the receiving port spaced therefrom.

Movement of a web edge in the edge entry gap and across the space between the ports varies the amount of air received by the receiving port and hence the pressure acting on the diaphragm. The valve member operates in response to the diaphragm movement to control pressurized fluid passing through the ports in the valve chamber and this fluid is used to actuate web-positioning means in response to web edge movement between the ducts. It will be evident that small pressure variations on the diaphragm maybe used to control large pressure variations in the fluid pressure system and damping of valve member by means of the diaphragm and receiving port, minimizes any tendency of the valve member to oscillate within the chamber and reduces its response time to achieve a principal objective of the invention.

A practical arrangement of the invention will now be described with reference to the accompanying drawings in which: 1

FIG. 1 is a cross-sectional view of a web edge-sensing device in accordance with the invention;

FIG. 2 is a plan view of the device shown in FIG. I;

FIGS. 3 and 4 are cross-sectional views taken on the lines 3-3 and 44 respectively of FIG. 2;

FIGS. 5, 6 and 7 are cross-sectional views taken on the lines S5, 6-6 and 77 respectively of FIG. 3; and

FIGS. 8 and 9 are block schematic diagrams of web material handling systems including a sensing device in accordance with the invention.

Referring now to the drawings, a pneumatic amplifying edge sensor is provided to yield a high air pressure output signal dependent on the position of a moving web edge.

The sensor shown in FIG. 1 comprises a body portion 9 for mounting by any suitable means 10 adjacent to a moving web and having a slot 11 into which the edge of the web (not shown) enters. Mounted within the bodyportion 9 is a removable, substantially cylindrical housing 12 having a recess 13, comprising part of the slot 11 when located in the body and a pair of elongated jets or ducts 14, 15 in spaced juxtaposition above and below the recess 13. The jets l4, 15 are accurately positioned and firmly fixed within the housing 12 such that by the release of suitable locking detent means 16 the housing 12 may be quickly removed from the sensor body 9 for cleaning purposes and instantly relocated therein without the need for further adjustment of the jets l4, l5. Mounted on the sensor body is a fluid control valve assembly 17 comprising a spool valve member '18 located in a cylinder 19, one extremity 20 of the spool valve member normally resting under the action of a very light spring 21 against one face of a diaphragm 22, this face being open to atmosphere.

The other face of the diaphragm communicates with an airspace 23 leading to the jet 15 in the housing 9.

The effective area of the diaphragm 22 is maximized by the inclusion of an inflexible metal plate 24 covering all but a flexible outer ring clamped at its outer edge 25 by cover plate 26. Low-pressure air is directed through the jet 14 across the edge-detecting slot 13 to impinge on the receiving jet is communicating with the diaphragm 22. Air pressure recovered by the receiving jet 15 acts on the diaphragm to move the spool valve member 18 within its cylinder 19 to control operation of i the valve 17 in a manner to be described hereinafter. Movement of a web edge into the web slot 13 will include portion or all of the air normally received by the receiving jet 1S and thus influence operation of the valve 17. This operation of the valve may be used to control known web-repositioning equipment. Referring now to FIGS. 3 to 7 valve body I7 comprises a cylinder 119 with a normally vertical axis having an elongated cylindrical spool valve member 18 located therein and as previously described the lower extremity of the spool valve member rests against one face of the diaphragm, 22. The spool valve member includes an intermediate portion 27 of reduced diameter. The valve body is provided with a fluid inlet port 28, a fluid outlet port 29 and a port 30 vented to atmosphere. The output air pressure is internally ported back via passage 31 to the top extremity of the spool 18 where it exerts a downward force on the spool equal to the product of the actual output pressure and the spool full sectional area.

As a practical example, the pressure applied to the lower jet 14 is approximately 15 in. water gauge and the pressure recovered at the upper jet 15 is of the order of 8 in. water gauge when the web is entirely free of the slit.

The feature of the invention is that this low pressure passes into a very small volume under the diaphragm 22 and is then linearly amplified to for example p.s.i. in a valve that can deliver a fairly large flow ofair in the order of 2 s.c.f.m. This means that the time which the recovered pressure takes to respond is very small because the volume to be filled is very small and any auxiliary equipment mounted some distance from the sensor can be rapidly filled with high-pressure air so that the expotential time constant of this operation is very low.

In fact time constants of the order of 20 milliseconds may be obtained.

With the dimensions of a particular sensor, the theoretical pressure gain is 320 but due to practical limitations such as valve leakage, and finite diaphragm elasticity, the gain is in fact approximately 250.

Thus in summary:

1. A low-pressure air jet and receiving orifice is used to detect the material edge, and the recovered pressure which depends on the edge position, is amplified by a large stable factor, using a force balance, high area ratio, pneumatic pressure amplifier.

2. By mounting the valve immediately over the jet receiving orifice the volume and thereby the pressure-equilibrating time in the input chamber of the valve is kept to an absolute minimum.

3. Very long narrow air jet and receiving orifices are used. They are both mounted in an easily removable cartridge which allows easy cleaning, while maintaining the necessary precision alignment between the two.

4. The long dimension of the jet and receiving orifices can be set at varying angles to the material edge, thereby giving a wide range of variation in the slope of the characteristic curve relating edge position to output pressure, without effecting system response times.

. In order to decrease the response inertia even further the transmission lines between the sensor and ancillary webpositioning equipment may be filled with a noncompressible fluid, .for example oil or hydraulic fluid. Thus in a practical situation where tubing of A inch bore is used for the pressure feed lines over a distance of 30 feet a response time constant of 5 milliseconds may be obtained compared with a response of about 150 milliseconds for the optimum air transmission line from the same sensor and ancillary equipment.

6. Referring now to FIG. 8 a practical web-positioning system incorporating a sensor in accordance with the invention is shown schematically.

The sensor 9 in the arrangement shown is used to control the edge position of an air transparent material for example woven cloth ,or the like and to permit normal operation of the sensor a mechanical edge sensing device is used comprising a material engaging flag" 32 biased against the edge (not shown) of the material by the piston and cylinder assembly 33. Air pressure from an air supply (not shown) is fed via valve 34 and filter 35 to the cylinder 32 to operate the piston and cylinder assembly 33. Similarly air from the supply is fed via lines 37 and 38 to the sensor jets and sensor valve respectively.

Operation of the sensor is controlled by a mechanical baffle 39 operable in response to movement of the flag 32. Air pressure output from the sensor 9 is conveyed by line 40 to a servo valve 41. The servo valve 41 is operative under the influence of the air output pressure from the sensor 9 to control movement of the piston 42 within cylinder 43, the piston 42 being moved within the cylinder 43 in a direction dependent on the application of oil under pressure in lines 44 and 45. The flow direction of the oil in these lines is controlled by the action servo valve 41 under the influence of the sensor air output pressure to direct oil pumped under pressure from the oil reservoir 46 by pump 47 via filter 48. The piston 42 may thus be used to operate known web-positioning equipment in response to movement of the edge-sensing flag 39. Where air opaque webs are to be controlled the flag 32 and associated equipment is not necessary and the web edge would enter the sensor in the manner hereinbefore described with reference to FIG. 1.

Referring now to FIG. 9 a pressure differential system is shown in which the possibility of system oscillation or hunting is substantially eliminated.

In the system shown a piston and cylinder assembly 49, 50 is connected with a pair of oil reservoirs 51, 52 by lines 53, 54.

Each of the reservoirs 51, 52 are connected via valves 55, 56 respectively with an air pressure supply (not shown) by line 60. Valves 55 and 56 are high flow pressure amplifiers with a gain of one and valve 56 is positive acting whilst valve 55 is negative acting. Associated with valve 55 is a bias coupler 57 connected via line 58 with a source of air pressure.

Valves 56 and 55 are also both connected via line 59 to the output of a sensor (not shown) in accordance with the invention.

ln operation of the system, output pressure from the sensor is fed to the valves 55 and 56 and for the purposes of explana-. tion a typical set of pressure values throughout the system will be included.

On the assumption that the output pressure range from the sensor is 0 to lb./sq.-ft. the piston 49 is arranged to be stationary within the piston 50 when an equal pressure of 40 lb./sq. in. acts on either side of the piston, the pressure on the left-hand side being negative due to the action of valve 55 and on the right-hand side positive due to the action of valve 56. Thus if the output from the sensor is 40 lb./sq. in. with the web running true, movement of the web into or out of the sensor gap will vary the static pressure of 40 lb./sq. in, within the system either above or below 40 lb./sq. in. to cause movement of the piston 49 within the cylinder 50 in a direction dependent on whether the deviation is above or below 40 lb./sq. in. The pressure acting on the piston is drawn from the supply through line 60 and in the example under consideration the supply pressure would be slightly greater than 80 lb./sq. in., while the bias pressure on valve 57 would be 80 lb./sq. in. As sensor pressure falls, valve 56 causes right side pressure to fall and at the same time valve 55 causes left side pressure to rise. As sensor pressure rises, the cylinder pressure trend reverses.

Movement of the piston may thus be used to control the positionv of known web-handling equipment and due to the very fast action of the valves 55 and 56, any tendency to oscillation or hunting is eliminated.

We claim:

1. An edge-sensing device comprising a body portion having an edge entry gap, a pair of ports in spaced juxtaposition in said entry gap, one of said ports being arranged to receive air discharged from the other port valve means mounted on the body portion of the sensing means and comprising a valve chamber having a fluid inlet port and a fluid outlet port, a port communicating with atmosphere and a valve member movable within the chamber in response to movement of the diaphragm to supply fluid from the inlet port to the outlet port or vent the outlet port to atmosphere, and a duct within the body to permit fluid pressure from the outlet to be applied to the valve member to control its movement against the action of the diaphragm in such a manner that the valve stabilizes in position only when the upward force from the diaphragm balances the downward force on the valve member so produced, the operation of the device being such that movement of a web edge in the edge entry gap across the space between the ports causes responsive movement of the diaphragm and hence operation of the valve means.

2. An edge-sensing device according to claim 1 wherein the ports in the body portion are fixed in a housing including at least part of the edge entry gap and removable from the body portion for maintenance purposes, locking means being provided to accurately locate the port housing within the body portion without the need for further adjustment.

3. An edge-sensing device according to claim I wherein one of the ports is connected with a source of compressed air and air discharged through this port is directed to the receiving port spaced therefrom.

4. A system for controlling the edge position of a moving web comprising an edge-sensing device wherein air pressure variations in the output of valve means actuated thereby are applied to further valve means operable to control the movement of hydraulically operated web-positioning means comprising a piston and cylinder assembly, movement of the piston within the cylinder being utilized to efiect a web path correction movement of a web roll or roll supporting stand and including mechanical baffle means disposed for movement within a sensor gap in the edge-sensing device said movement being efi'ected through a linkage by web edge con- (acting means remote from said gap.

5. A system for controlling the edge position of a moving web comprising an edge-sensing device wherein air pressure variations in the output of valve means actuated thereby are applied to further valve means operable to control the movement of hydraulically operated web-positioning means, comprising a piston and cylinder assembly, movement of the 

1. An edge-sensing device comprising a body portion having an edge entry gap, a pair of ports in spaced juxtaposition in said entry gap, one of said ports being arranged to receive air discharged from the other port valve means mounted on the body portion of the sensing means and comprising a valve chamber having a fluid inlet port and a fluid outlet port, a port communicating with atmosphere and a valve mEmber movable within the chamber in response to movement of the diaphragm to supply fluid from the inlet port to the outlet port or vent the outlet port to atmosphere, and a duct within the body to permit fluid pressure from the outlet to be applied to the valve member to control its movement against the action of the diaphragm in such a manner that the valve stabilizes in position only when the upward force from the diaphragm balances the downward force on the valve member so produced, the operation of the device being such that movement of a web edge in the edge entry gap across the space between the ports causes responsive movement of the diaphragm and hence operation of the valve means.
 2. An edge-sensing device according to claim 1 wherein the ports in the body portion are fixed in a housing including at least part of the edge entry gap and removable from the body portion for maintenance purposes, locking means being provided to accurately locate the port housing within the body portion without the need for further adjustment.
 3. An edge-sensing device according to claim 1 wherein one of the ports is connected with a source of compressed air and air discharged through this port is directed to the receiving port spaced therefrom.
 4. A system for controlling the edge position of a moving web comprising an edge-sensing device wherein air pressure variations in the output of valve means actuated thereby are applied to further valve means operable to control the movement of hydraulically operated web-positioning means comprising a piston and cylinder assembly, movement of the piston within the cylinder being utilized to effect a web path correction movement of a web roll or roll supporting stand and including mechanical baffle means disposed for movement within a sensor gap in the edge-sensing device said movement being effected through a linkage by web edge contacting means remote from said gap.
 5. A system for controlling the edge position of a moving web comprising an edge-sensing device wherein air pressure variations in the output of valve means actuated thereby are applied to further valve means operable to control the movement of hydraulically operated web-positioning means, comprising a piston and cylinder assembly, movement of the piston within said cylinder being utilized to effect a web path correction movement of a web roll or roll-supporting stand, said piston and cylinder assembly being actuated by fluid under pressure from a pair of fluid reservoirs, pressure in each reservoir being controlled by high flow pressure amplifier valves connected with a source of air pressure, the supply of air pressure by the amplifier valves to the reservoirs being controlled by air pressure output from the edge-sensing device. 